Evidence supporting a relationship between stress and reveals increased rates of dexamethasone resistance and basal hypersecretion of glucocorticoids in normal elderly humans. This relationship has been revealed in clinical studies which are highly relevant, however this approach does not permit the specificity of variables or degree of control which may be obtained using animal models. Comparing older and prime aged female rhesus monkeys in a series of studies has provided a specific test of hypotheses regarding 1) the ability of old females to adapt to stress, 2) the effect of stress on the pituitary-adrenocortical axis and the immune system (using functional measures), 3) the effect of social companionship and reactivity in modulating stress and 4) the effect of HRT on immune system measures in ovariectomized females. During this past year studies have been directed toward assessment of factors that have been shown to predictive of immune perturbation in aging in dividual s. These experiments demonstrated differences in stress reactivity, as indicated by changes in immune function, between prime and old age rhesus monkeys, confirming the primary hypothesis. This observation is consistent with a literature suggesting that aging is characterized by a decreased ability of individuals to adapt to stress, a decrement that is linked is linked to hypothalamic-pituitary-adrenal axis dysregulation. FUNDING NIH / AG13722 $133,704 12/01/1996 - 11/30/99 PUBLICATIONS None P51RR00165-38 1/1/98 - 12/31/98 Yerkes Regional Primate Research Center